Although stealth technology has come a long way, invisibility has remained largely confined to the world of fiction.

However, as recently reported in the online journal, Scientific
Reports ( www.nature.com/srep), some Iowa State University
( www.iastate.edu) students appear to have taken a significant
step in that direction. Working on the theory that
electromagnetic waves — and possibly short wavelengths of
visible light — can be suppressed using flexible, tunable liquid-metal materials, they developed a stretchable polymer “
meta-skin” that can be tuned to reduce reflections over a wide range
of radar frequencies.

The skin consists of rows of split ring resonators embedded
in silicone sheets. The electric resonators are filled with
Galinstan®: a commercial liquid metal alloy of mostly gallium,
indium, and tin. Each resonator is a ring with a radius of 2. 5 mm
and a thickness of 0.5 mm. The rings have a 1 mm gap, which
in effect creates a curved segment of liquid wire. According to
the journal report, “The rings create electric inductors, and the gaps create electric capacitors. Together, they create a
resonator that can trap and suppress radar waves at a certain frequency. Stretching the meta-skin changes the size of
the liquid metal rings inside and changes the frequency the devices suppress.”
Radar suppression was reported to be about 75 percent in the 8 to 10 GHz range. When objects are wrapped in
the meta-skin, the radar waves are suppressed in all incident directions and observation angles. Presumably, similar
meta-skin could be used to coat future stealth aircraft, but the researchers have their sights set on a higher goal: a cloak
of invisibility. According to Asst. Prof. Liang Dong, “The long-term goal is to shrink the size of these devices. Then,
hopefully we can do this with higher frequency electromagnetic waves such as visible or infrared light.” ▲

ADVANCED TECHNOLOGY

Diodes in Your DNA

It’s no secret that we’ve been pushing the physical limits of silicon for years, and silicon-based circuits can’t get much smaller without
becoming unstable. Looking for alternatives, researchers at the
University of Georgia ( www.uga.edu) and Israel’s Ben-Gurion
University of the Negev ( in.bgu.ac.il) have discovered that nanoscale
electronic components can be made from single DNA molecules.

According to UGA College of Engineering Prof. Bingqian Xu, DNA's
predictability, diversity, and programmability make it a leading
candidate for the design of functional electronic devices using single
molecules.

Specifically, Xu and colleagues isolated a specifically designed
single duplex DNA of 11 base pairs and connected it to a circuit
measuring only a few nanometers. After inserting a small molecule of
the chemical coralyne, they found that the current flowing through
the DNA was 15 times stronger for negative voltages than for positive,
thereby acting as a diode. According to Xu, “Our discovery can lead
to progress in the design and construction of nanoscale electronic
elements that are at least 1,000 times smaller than current
components.”
Research is continuing with the goal of building additional molecular devices
and enhancing the performance of the molecular diode which may pave the way to
a generation of smaller more powerful advanced electronic devices. ▲
■ BY JEFF ECKERT TECHKNOWLEDGEY 2016

■ This flexible meta-skin can trap radar waves
and cloak objects.

■ Illustration of DNA
junction used to create a
single molecule diode.